I have a 2004 BMW 318d Touring, and there were a couple of advisory items marked on my last MOT test report a few weeks ago. I’ve done a fair bit of car DIY in the past, although I’ve become a bit lazy in recent years, but now I have a bit more spare time. So I wondered if The Doctor might advise me of the practicality of undertaking these two jobs? 

What I have marked down are “front brake reaction arm bushes” suggested as needing replacement, and “brake fluid replacement”. I asked on what basis the latter item had been identified, and I was told that the fluid in the reservoir looked rather discoloured – and I certainly haven’t had the fluid changed in the four years that I’ve owned this excellent car. I could not dispute the suspension bush item as they said that the bushes were looking perished, but not too bad, but that when they get old like this it allows too much movement in the suspension arm and the possibility of resulting in uneven tyre wear. I’m hoping this is in your knowledge bank Doc and that you will be able to tell me to either have a go at the two jobs, or maybe to leave well alone! Thanks in anticipation. 

Dick Newton, Derby

Well Dick, you haven’t caught me too cold on these two items and I think I can offer you some helpful advice. Let’s deal with the brake fluid change first. For readers who are not wise to the necessity of a regular brake fluid change, generally every two or three years, this is because brake fluid picks up water from the atmosphere (it’s hygroscopic if you want a posh word!) and this progressively degrades its performance by reducing the boiling point. Many people will get by without problems without sticking to this wise advice, but if you drive your car hard and live in a hilly area, you might live (hopefully!) to regret ignoring my advice. With heavy braking, the brake fluid can get very hot, maybe even boil, and then seriously lose braking performance, as you’ll find when the pedal goes very soft, or right down to the floor. Anyway, I would suggest Dick that, unless you’ve already got the kit for this job, which means some bottles, some suitable plastic tubing, and a very patient partner (this is normally a two-person job, without specialist equipment), that you leave this to a local garage or repairer. If you had done the job before you would not be asking me this question, and I think, for that reason alone, I would suggest that you leave it to a professional. It won’t cost too much in any case. 

On the other hand, if you are young, fit, and still have a decent tool kit, I reckon the suspension bush job would save you some money and keep you out of trouble for a weekend afternoon – although I know it’s probably only a one-hour plus job for an experienced mechanic. First thing would be to take a front wheel off and look at the suspension. You will see a suspension arm that has two ball joints, at the front and middle, and at the rear the arm fits into a bush that fits into a housing that is bolted (two bolts) to the front chassis frame. Your task Dick (should you choose to accept it!), is to unbolt the bush from its housing, and merely replace it with a new unit on each side. They are usually called suspension control arm bushings or, more correctly in BMW-speak, brake reaction arm bushings, and you can buy a set of left and right with new bolts for around £40 plus on Amazon UK. You will want BMW part number 3112 678 3376 for the set of two, which is two (left and right) bushes in their housings. 

So it’s road wheel off, possibly the front under-tray off (it varies within the range of the E46 3-Series) for access, then the bushing bolts off; then comes the worst bit; that’s persuading the old bushes off the suspension bar end, as they may be quite firmly stuck, and start to break up when you remove them. Anyway, a bit of soap and a soft hammer, or even a bearing puller may help, and you certainly will want a bit of (non oily – like soapy liquid) lubrication to help push the correct new bush and housing (left or right) fully onto the suspension arm (after you’ve cleaned off the end), ensuring the correct alignment so that the housing lines up with the mounting holes. There are flats on the arm end where the bush slides on, because the bush is voided to allow more compliance in one plane. You might possibly then need to use a bit of persuasion to line things up, and get the threads started, but then the job’s just about done. Oh no! You’ve now got the other side to do! But then that will only take you half the time, unless you’ve skinned a knuckle on the first one! 

Have fun Dick – I’m sure you’ll enjoy the satisfaction of the DIY job, and your Beemer will probably steer and brake a bit more precisely when you get back on the road. Good luck. 

Doc Diesel

(P.S. Don’t e-mail on a Sunday and tell me that you’re stuck!)